newfs_msdos: allow to work with media that doesn't have any CHS params

Either use parameters provided by user or make them up.
The code for faking CHS params is borrowed from disklabel code.
The logic for using user-provided and auto-guessed parameters is not
perfect, so to speak.

PR:		bin/121182
Approved by:	jhb (mentor)

1 files changed, 17 insertions, 5 deletions

diff --git a/sbin/newfs_msdos/newfs_msdos.c b/sbin/newfs_msdos/newfs_msdos.c
index 9c021c028381..1a8b81f23eda 100644
--- a/sbin/newfs_msdos/newfs_msdos.c
+++ b/sbin/newfs_msdos/newfs_msdos.c
@@ -793,13 +793,25 @@ getdiskinfo(int fd, const char *fname, const char *dtype, __unused int oflag,
     /* Maybe it's a fixed drive */
     if (lp == NULL) {
 	if (ioctl(fd, DIOCGDINFO, &dlp) == -1) {
-	    if (ioctl(fd, DIOCGSECTORSIZE, &dlp.d_secsize) == -1)
+	    if (bpb->bps == 0 && ioctl(fd, DIOCGSECTORSIZE, &dlp.d_secsize) == -1)
 		errx(1, "Cannot get sector size, %s", strerror(errno));
-	    if (ioctl(fd, DIOCGFWSECTORS, &dlp.d_nsectors) == -1)
-		errx(1, "Cannot get number of sectors, %s", strerror(errno));
-	    if (ioctl(fd, DIOCGFWHEADS, &dlp.d_ntracks)== -1)
-		errx(1, "Cannot get number of heads, %s", strerror(errno));
+
+	    /* XXX Should we use bpb->bps if it's set? */
 	    dlp.d_secperunit = ms / dlp.d_secsize;
+
+	    if (bpb->spt == 0 && ioctl(fd, DIOCGFWSECTORS, &dlp.d_nsectors) == -1) {
+		warnx("Cannot get number of sectors per track, %s", strerror(errno));
+		dlp.d_nsectors = 63;
+	    }
+	    if (bpb->hds == 0 && ioctl(fd, DIOCGFWHEADS, &dlp.d_ntracks) == -1) {
+		warnx("Cannot get number of heads, %s", strerror(errno));
+		if (dlp.d_secperunit <= 63*1*1024)
+		    dlp.d_ntracks = 1;
+		else if (dlp.d_secperunit <= 63*16*1024)
+		    dlp.d_ntracks = 16;
+		else
+		    dlp.d_ntracks = 255;
+	    }
 	}
 
 	hs = (ms / dlp.d_secsize) - dlp.d_secperunit;